The method and apparatus of the present invention relates to plotters which may be used for generating images or drawing lines on light sensitive material by means of a light beam or spot movable over the light sensitive material. In prior art plotting apparatus such as disclosed in U.S. Pat. Nos. 3,330,182 and 4,209,239 and having the same assignee as the present invention, an optical light head is moved relative to a sheet of light sensitive material and selectively exposes the material in order to produce a plot of graphic information. The selective exposure occurs by projection of a beam of light from the head onto the sheet material to produce a light spot and then moving the sheet material and light head relative to one another to move the spot along a predetermined path and expose the sheet material correspondingly. The exposed material, when photographically developed, bears a line trace corresponding to the path traversed by the light spot and having a width corresponding to the width of the spot. Line traces can also be produced by flashes of the light beam at consecutive positions on the sheet material. Additionally, individual flashes at selected locations on the sheet material expose the light sensitive material in accordance with the shape of the light spot.
In U.S. Pat. Nos. 3,330,182 and 4,209,239, referenced above, an aperture plate is provided in the plotting apparatus with a plurality of individual apertures of different sizes and shapes. The apertures are situated in a serial array on the aperture plate so that plate movement brings the apertures individually into a position between a light source in the light head and light sensitive material. When the plotting apparatus is in operation, the light source projects a light beam through a selected aperture and, by suitable optical means, the image of the aperture is focused onto the light sensitive material so that the size and shape of the aperture determines the graphic image produced.
Movement of the plate having the plurality of apertures, as in the referenced patents may be accomplished by use of a drive mechanism, such as a drive motor with suitable gearing, which engages the plate. The drive mechanism is controlled by a device, such as a computer, which is programmed to cause a desired aperture to be positioned in the path of the projecting light beam. Commonly, the device controlling the photoplotting operation is programmed to position the aperture plate in accordance with a particular location in the array of apertures where a desired aperture is expected to be. Should the desired aperture not be positioned in the programmed location, the controlling device does not recognize the problem, and the plotting operation continues in error. Since several adjustable image characteristics and the final plot are dependent upon the desired aperture being in its programmed location in the array, faulty line traces on the sheet material result if the apertures are improperly placed or missing.
It is, therefore, a general object of the present invention to provide a plotting apparatus and method for changing the characteristics of the image projected onto a light sensitive material by basing the control of the image-generating operation upon identification of individual image characteristics produced by the optical head.
It is a further object of the invention to incorporate into the plotting apparatus a system which causes adjustment of the light characteristics or other components in the apparatus to be based on the identity of optical modifiers in the head.